Cross member for vehicle bumper bar and method for making same

Abstract

A two step system or stage is provided to manufacturer a bumper of “B” shape cross section including a roll forming-welding stage where a straight cross member of a length to mount on the front or rear of various models of automobiles and the bending stage where any curvature or sweep is introduced into the cross member as required by the design of the automobile. The roll forming welding stage include the spot or tack welding of the front wall to the web followed immediately by welding together without any gaps therebetween the abutting longitudinal edges utilizing a high frequency welder. Thus, the “B” shaped cross section of the bumper may be used to make different bumpers of various lengths and curvatures.

Description

CROSS REFERENCE TO RELATED APPLICATION [0001] This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60 / 539,511 filed Jan. 26, 2004.1. FIELD OF THE INVENTION [0002] This invention relates to a roll formed tubular vehicle cross member, bumper beam or bar fabricated from high or ultra-high strength steel. The cross member may be either straight or provided with a sweep or curvature having a value of more than 10. The resulting tubular bumper has a high impact resistance, low weight and relatively low cost of manufacture. 2. BACKGROUND OF THE INVENTION [0003] Bumper beams or cross members for vehicles, particularly automobiles, are made from high strength or ultra-high strength steel. It has been difficult to manufacture the bumper beam or bar out of some high strength steel because such bar requires a curvature to be placed therein. It is necessary to roll form the cross member to obtain the desired curvature. In the past, when high strength steel is roll ...

AI Technical Summary

Benefits of technology

The present invention provides a method and equipment for making a tubular cross member of B shape from high strength or ultra-high strength steel. The cross member can be made from a variety of steels of varying thickness, cut to different lengths, and bent to different curvatures for various automobiles. The same roll formers are used for different length and curvature bumpers, which provides an economical advantage over prior art methods. The method includes roll forming the cross member from a single sheet of steel, spot welding the front and rear walls, connecting the inner side walls with a roll formed web, and welding the abutting longitudinal edges together. The cross member can be placed in a gravity stacking system and then manually or automatically placed in a curved state for use in bumpers. The method also includes a unique method of forming a straight tubular cross member by using a rolling spot or tact weld process to connect portions of the cross member to the web, followed by the in-line high frequency butt welding process to join the longitudinal edges.

Problems solved by technology

It has been difficult to manufacture the bumper beam or bar out of some high strength steel because such bar requires a curvature to be placed therein.

In the past, when high strength steel is roll formed into the desired sweep or curvature, the material of the cross members has been damaged during the process resulting in unacceptable quality.

Formability of high strength steel is difficult than with low carbon steels because of greater spring-back and reduced ductility.

A disadvantage of the methods and apparatuses disclosed in the Sturrus and Sturrus et al patents is that the method and apparatus for forming the straight tubular “B” section cross member and the equipment for forming the sweep in the cross members are connected together in one line, with the severing of the cross member from the roll formed member being located down stream of the welding station.

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